CHST CHST - Construction Health and Safety Technician Excavation and Trenching Safety Questions and Answers 5 — Questions and Answers
Question 1: A contractor uses timber shoring in a 9-foot deep trench. OSHA Appendix C tables indicate the uprights should be spaced at a maximum of 8 feet apart. The contractor spaces them 10 feet apart. What is the violation?
- No violation if the soil is Type A
- Failure to follow manufacturer specifications
- Failure to comply with tabulated data, which is a violation of 29 CFR 1926.652 (Correct answer)
- Acceptable if a competent person approves the spacing
Correct answer: Failure to comply with tabulated data, which is a violation of 29 CFR 1926.652
Tabulated data in OSHA Appendix C must be followed as written; exceeding the maximum spacing undermines the engineered protection and violates 29 CFR 1926.652.
Question 2: What term describes the failure of a large mass of soil on the side of an excavation that slides in and rotates downward due to the weight of the soil above?
- Heave
- Boiling
- Rotational slide (slump failure) (Correct answer)
- Lateral squeezing
Correct answer: Rotational slide (slump failure)
A rotational slide (slump failure) occurs when a curved failure plane develops and a mass of soil rotates and slides into the excavation.
Question 3: Which of the following correctly describes 'heave' in the context of excavation hazards?
- Groundwater rushing into the trench bottom
- Upward movement of the trench bottom caused by soil pressure differential (Correct answer)
- Lateral movement of trench walls inward
- Tension cracking at the surface near the trench edge
Correct answer: Upward movement of the trench bottom caused by soil pressure differential
Heave is an upward bulging of the trench bottom caused by the weight of soil on the sides exceeding the bearing capacity of the material below the trench floor.
Question 4: Under OSHA standards, what action is required when a water accumulation hazard exists in a trench?
- Workers may continue if wearing waterproof boots
- Workers must not enter until water is controlled and a competent person has assessed the situation (Correct answer)
- Install pumps and continue normal operations
- Shore the walls and proceed
Correct answer: Workers must not enter until water is controlled and a competent person has assessed the situation
OSHA 29 CFR 1926.651(h) prohibits workers from entering excavations with accumulated water unless water control measures are taken and a competent person approves re-entry.
Question 5: Which type of shoring uses steel plates driven into the ground before excavation begins to prevent soil movement?
- Hydraulic shoring
- Trench box (shield)
- Sheet piling (Correct answer)
- Timber shoring
Correct answer: Sheet piling
Sheet piling consists of interlocking steel sheets driven vertically into the ground prior to excavation to retain soil and groundwater.
Question 6: A competent person must have which TWO characteristics according to OSHA's definition?
- A college degree and 5 years of experience
- Knowledge to identify existing and predictable hazards AND authority to take corrective action (Correct answer)
- OSHA 30-hour certification and a PE license
- First aid certification and supervisor status
Correct answer: Knowledge to identify existing and predictable hazards AND authority to take corrective action
OSHA defines a competent person as one who can identify hazardous conditions and has the authority to eliminate them promptly (29 CFR 1926.32(f)).
Question 7: Which scenario most accurately describes a 'fissured' soil condition that affects soil classification?
- Soil that is damp and cohesive with no visible cracks
- Soil with a high clay content that retains shape when squeezed
- Soil with cracks or tension fractures visible in the trench wall (Correct answer)
- Soil that has been compacted by heavy machinery
Correct answer: Soil with cracks or tension fractures visible in the trench wall
Fissured soil contains visible cracks or fractures that indicate internal failure planes, reducing its cohesive strength and requiring reclassification to Type B or C.
CHST CHST - Construction Health and Safety Technician Excavation and Trenching Safety Questions and Answers 5
A contractor uses timber shoring in a 9-foot deep trench.
OSHA Appendix C tables indicate the uprights should be spaced at a maximum of 8 feet apart.
The contractor spaces them 10 feet apart.
What is the violation?